Pressure responsive centralizer

ABSTRACT

A centralizer including hollow structural components. In at least one embodiment, the hollow structural component is sealed by at least one valve or rupture disk. When unacceptable overpressures occur, the valve or rupture disks break to allow influx into the hollow element, thereby relieving pressure and avoiding damage that might otherwise occur. In other embodiments, the hollow structural component collapses to expand available volume.

FIELD OF THE INVENTION

The present invention relates to systems and methods for controllingpressure in wellbores.

BACKGROUND AND SUMMARY OF THE INVENTION Background: Pressure in Well

Annular pressure buildup within wellbores has been recognized in the oiland gas industry for many years as a serious problem. Fluids trapped ina wellbore or annular space in a wellbore will expand with acorresponding increase in temperature leading to a volume increase andincrease in the force they exert upon the surrounding area. Thispressure has been known to be a significant factor in the failure ofsubsea wells, including Well A-2 of British Petroleum 1999 Marlindevelopment program in the deepwater program off the Gulf of Mexico. Onerelevant article is Practical and Successful Prevention of AnnularPressure Buildup on the Marlin Project, SPE International 77473, 2002,Richard F. Vargo, Jr., et al, and which is hereby incorporated byreference in its entirety.

Background: Annular Pressure Build Up

Annular pressure buildup (“APB”) is the pressure generated by thermalexpansion of trapped fluids as they are heated. When wellbore fluidsheat up and expand in a closed system, the expansion causes high inducedpressures. Most land and many offshore locations may be able to bleedthis pressure through surface-accessible wellhead equipment. In subseacompletions, the primary annulus between the tubing and productioncasing may be the only accessible annulus. Consequently, bleeding theouter annuli may not be possible. Therefore, when the risk of subsea APBexists, well designers should give serious consideration to appropriatemitigation as part of the fundamental well design.

Offshore hydrocarbon recovery operations are increasingly moving intodeeper water and more remote locations. Often satellite wells arecompleted at the sea floor and are tied to remote platforms or otherfacilities through extended subsea pipelines. Some of these pipelinesextend through water that is thousands of feet deep, where temperaturesof the water near the sea floor are in the range of about 40° F. Thehydrocarbon fluids, usually produced along with some water, reach thesea floor at much higher temperatures, characteristic of depthsthousands of feet below the sea floor.

In order for a well to experience APB, two conditions are generallyknown to be present. First, there must be a sealed region, typically anannulus, wherein pressure may build. Second, a temperature rise isgenerally associated with the increase in pressure.

Background: General APB Mitigation Techniques

Several existing solutions have been presented in past literature. Thesesolutions include:

-   -   cement shortfall (leave cement short of previous casing);    -   providing a leak path or bleed port;    -   syntactic, crushable foam wrap;    -   compressible fluids placed in the trapped annulus to absorb        volume;    -   heavyweight and/or high-yield casing (enhanced casing design);        and    -   full-height cementing (cement filling the entire annulus).

These can be incorporated into drilling plans to mitigate APB risks insome circumstances. A good starting point is to try to ensure that theannulus does not become trapped. Whenever possible, cement shortfall isusually designed. This assumes that cement heights will be below theprevious casing shoe and that a trapped annulus condition may not occur.However, cement can still channel because of poor mud displacement. Suchdisplacement problems are caused by poor casing eccentricity or poorerodibility of the wellbore fluids during the primary cementingoperation. In addition, barite sag following drilling can cause atrapped condition. A trapped condition can occur either by cementitiousmaterials or due to the settling of weighting materials from the mud. Inmany cases, subsea wells are drilled and left to be completed at a laterdate because of the lead time required for other components of theproduction infrastructure, i.e. pipelines, etc. Over time, the solids inthe mud can settle out, creating a trapped condition. Later when thewell is completed, the trapped annulus condition and the resulting APBmay not show up until a failure occurs.

A second APB prevention technique consists of attaching syntacticcrushable-foam wrap to the casing. The syntactic foam contains small,hollow glass spheres filled with air at atmospheric pressure. When ABPreaches a certain level, the hollow spheres collapse. This collapseresults in a correspondent increase in available volume to therebydecrease pressure. Data demonstrate that the volume required for aneffective solution is about 2% to about 8% of the annular volume.

Another way of prevention of APB is the use of compressible fluids inthe trapped annulus to absorb volume increases as the heat up occurs.

A final way of mitigating APB is by using enhanced casing products.Increased casing capacities can accommodate a higher degree of pressurebuildup without detrimental effects to the casing or well. Extensivework has been applied here also involving advanced, probabilisticperformance properties of the subject casings.

Pressure Responsive Centralizer System

The present inventions describe methods and systems for controllingpressure and volume variations in boreholes. For example, in oneembodiment an innovative centralizer comprises a centralizing structurewith at least one sealed hollow structural component where a rupturedisk is capable of breaking in response to sufficient pressure. Thepresent innovations further teach a method of effecting a volumetricchange in response to overpressure within a wellbore comprising at leastone hollow structural component. The present innovative systems andmethods can be used to avoid production loss due to wellbore damage orthe need to restrict hydrocarbon flow in an effort to keep productiontemperature below danger levels.

Another advantage of the disclosed centralizer is the ability to beconnected to the drilling and production equipment in a number of ways.The centralizer can be fitted with a rupture component made part of thecentralizer, screwed into the bottom of the centralizer by means ofthreads within the centralizer, or connected by some other means.

It should, of course, be understood that the description is merelyillustrative and that various modifications and changes can be made inthe structure disclosed without departing from the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed inventions will be described with reference to theaccompanying drawings, which show important sample embodiments of theinvention and which are incorporated in the specification hereof byreference, wherein:

FIGS. 1 a and 1 b show a preferred embodiment of a centralizer.

FIG. 2 shows a preferred embodiment of a centralizer.

FIG. 3 shows a preferred embodiment of a centralizer configuration usinga ‘hinged’ arrangement within a bore.

FIG. 4 shows a production system using a centralizer with hollow rupturecomponents.

FIG. 5 shows a preferred embodiment of a centralizer with multiplerupture components.

FIG. 6 shows a preferred embodiment of a pressure responsive system witha centralizer and multiple rupture components.

FIG. 7 shows a preferred embodiment of a hollow rupture component.

FIG. 8 shows a preferred embodiment of a centralizer where an emptyrupture component is affixed to the main chamber of the centralizer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferredembodiment (by way of example, and not of limitation).

The disclosed inventions take advantage of a new way in which thepressure in boreholes can be controlled. In one embodiment, acentralizer is combined with a rupture disk to allow for the release ofexcess pressure from a wellbore. The hollow components in thisembodiment contain a burst disk or rupture disk, which are selected torupture at a predetermined pressure as required by well hydrostaticpressure and other factors. The inside and outside diameters of thecentralizer preferably provide effective centering of the casing in theborehole or outer casing. The number of struts and rupture and burstdisks may be adjusted in such a way as to meet the specific pressure andvolume needs of a specific project. For instance, in one embodiment,there may be six struts with one rupture disk in each strut. In anotherembodiment, there may be four struts with two rupture disks in eachstrut.

In another embodiment, a centralizer is combined with a relief valve inorder to allow for the release of excess pressure from a wellbore. Thehollow components in this embodiment contain a relief valve that isselected to open at a predetermined pressure as required by wellhydrostatic pressure and other factors. A relief valve is something thatis not destroyed when it opens. A hollow structural component is aprefabricated rigid structure capable of allowing for volumetricexpansion.

In yet another embodiment, the rupture disk is sealed in such a way asto ‘burst’ at a predetermined pressure to facilitate the production ofhydrocarbons. This invention avoids production loss due to wellboredamage due to overpressures and the need to restrict hydrocarbon flow inan effort to keep production temperature below danger levels.

In a further embodiment, the centralizer may also comprise at least onecentralizing structure and include at least one breakable structuralcomponent that can respond to pressure increase surges. The breakablestructural component can collapse, burst, or rupture to provide a volumechange in response to overpressure.

One advantage of this embodiment is that pressures build up withinboreholes can be alleviated. Another advantage is that the volume in awell can be controlled in such a manner as to optimize the productionwithin a well.

FIG. 1 a shows a sample preferred embodiment of the centralizer unit100. This is a side view of the centralizer unit itself, not showing thecasing which, once the centralizer 100 has been installed, wouldnormally pass through the axial central cavity 130. The struts 110 ofthe centralizer 100, in this embodiment, run parallel with the wellbore140. One or more rupture disks (not shown in this figure) are located inone or more of the struts. These struts are hollow structuralcomponents. In this embodiment, the centralizer is made of stainlesssteel. Carbon steel, chrome-moly, or titanium or other materials can beused instead.

FIG. 1 b shows a sample preferred embodiment of one of the struts 110 ofthe centralizer unit 100. This is a formed shape of tubular steel,having a hollow center (not visible in this figure). A rupture disk 112blocks the sole opening into the hollow center of strut 110. (Preferablya hole is drilled and tapped in the strut 110.) In this embodiment, theend of strut 110 is attached to circumferential element 120 by a weld114, which also serves to close off the hollow within the strut 110. Inthis embodiment the centralizer is made of stainless steel. Carbonsteel, chrome-moly, or titanium or other materials can be used instead.

FIG. 2 shows a sample preferred embodiment of the pressure responsivesystem using centralizer unit 200. This is a side view of thecentralizer unit itself, not showing the casing which, once thecentralizer 200 has been installed, would normally pass through theaxial central cavity 230. The struts 210 of the centralizer, in thisembodiment, run parallel with the wellbore 240. One or more rupturedisks (not shown in this figure) are located in one or more of thestruts. In this embodiment, the centralizer is made of stainless steel.Carbon steel, chrome-moly, or titanium or other materials can be usedinstead. In this embodiment, a centralizer is attached to the rupturecomponent using threads 260.

FIG. 3 shows a sample preferred embodiment of the centralizer unit 300.This is a side view of the centralizer unit itself, not showing thecasing which, once the centralizer 300 has been installed, wouldnormally pass through the axial central cavity 330. The struts 310 ofthe centralizer, in this embodiment, run parallel with the wellbore 340.One or more rupture disks (not shown in this figure) are located in oneor more of the struts. In this embodiment, the centralizer is made ofstainless steel, but or course carbon steel or chrome-moly or titaniumor other materials can be used instead. In this embodiment, acentralizer is attached to the rupture component using hinges 360.

FIG. 4 shows a production system 400 using a centralizer 410 with hollowrupture component 420 surrounded by wellbore 440. A casing used to movethe desired hydrocarbons or other material is illustrated by 470 inwhich hydrocarbons or other desired products may be moved from the wellto some kind of recovery equipment located at 480.

FIG. 5 shows a centralizer system 500 with multiple rupture components510, 520, and 530. Rupture components 510, 520, and 530 are attached tothe centralizer component 540. Centralizer component 540 is attached tohollow struts 550. Rupture components 510, 520, and 530 may be ofdifferent sizes and pressure sensitivities.

FIG. 6 shows a casing combination with centralizer and hollow rupturecomponents. A hollow component 600 contains multiple rupture components610 and 630. Within said hollow component walls 640 a hole is drilledand the first rupture component is placed at 610. A second rupturecomponent 630 is held in place by elements within the hollow componentat 620.

FIG. 7 shows a hollow rupture component 700. A ring 710 separates thesealed disc components 720 and 730. Hinges 740 can attach hollow rupturecomponent to the centralizer system. Hollow rupture component can alsobe attached by means of threads found at 750.

FIG. 8 shows a centralizer system 800 with a rupture component 810located at either end of the centralizer system 850 or 860. Additionalrupture components may be placed at 820, 830, and 840. The structuralcentralizer support struts 850 are placed along the bore.

In one example, the present innovations are enabled as a downholepressure adjusting system, comprising a centralizing structure and atleast one closed hollow structural component wherein the hollowstructural component is responsive to overpressure is claimed.

In another example, the present innovations are enabled as a downholepressure adjusting system, comprising a structure for placement on adownhole casing wherein the structure includes at least one hollowstructural component wherein the hollow structural component is sealedby means of one or more seals is also claimed.

In another example, the present innovations are enabled as a productionsystem, comprising a casing and a centralizer which includes at leastone hollow structural component is also claimed.

None of the description in the present application should be read asimplying that any particular element, step, or function is an essentialelement which must be included in the claim scope: THE SCOPE OF PATENTEDSUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS.

MODIFICATIONS AND VARIATIONS

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a tremendous range of applications, and accordingly the scope ofpatented subject matter is not limited by any of the specific exemplaryteachings given.

The pressure responsive system may be made out of any number ofmaterials, including, but not limited to, stainless steel, carbon steel,titanium, or any number of other materials. In addition, the number ofstruts, rupture disks, and relief valves may vary from embodiment toembodiment. The downhole string may be in different forms, including,but not limited to a tubular string or casing string.

One variation includes replacing the rupture disks with relief valves orother structures that will allow the enclosed volume to open at apredetermined pressure.

A particular advantage of the hollow chamber (at atmospheric pressure orpressurized) to be transported to a downhole location with a rupturedisk is that it can be designed to rupture at a predetermined stage ofoperations.

Note that the pressure required for rupture will correspond directlywith the internal design of the centralizer and the pressure with whichit is sealed at.

The hollow structural component may be physically part of thecentralizer, or be attached thereto, or may be separate from thecentralizer itself.

None of the description in the present application should be read asimplying that any particular element, step, or function is an essentialelement which must be included in the claim scope: THE SCOPE OF PATENTEDSUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS.

1. A downhole pressure adjusting system, comprising: a centralizingstructure; and at least one closed hollow structural component, whereinthe hollow structural component is responsive to overpressure.
 2. Thesystem of claim 1 wherein the hollow structural component is sealed byone or more rupture disks.
 3. The system of claim 1 wherein the hollowstructural component is sealed by one or more valves.
 4. The system ofclaim 1 wherein the hollow structural component at least partiallycollapses in response to pressure.
 5. The system of claim 1 wherein thecentralizing structure provides radial positioning of a casing and axialsupport within a wellbore.
 6. The system of claim 1 wherein thecentralizing structure provides radial positioning of a casing.
 7. Thesystem of claim 2 further comprising a second hollow structuralcomponent.
 8. The system of claim 2 wherein the rupture disk of thehollow structural component ruptures to relieve overpressure.
 9. Thesystem of claim 3 further comprising a second hollow structuralcomponent.
 10. A downhole pressure adjusting system, comprising astructure for placement on a casing, wherein the structure includes atleast one hollow structural component, and the hollow structuralcomponent is sealed by at least one seal.
 11. The system of claim 10wherein the seal is a rupture disk or a relief valve.
 12. A productionsystem, comprising: a casing; and a centralizer which includes at leastone hollow structural component.
 13. The system of claim 12 wherein thehollow structural component is sealed by a rupture disk.
 14. The systemof claim 12 wherein the hollow structural component is sealed by arelieve valve.
 15. The system of claim 12 wherein the hollow structuralcomponent is designed to collapse at a predetermined pressure.
 16. Thesystem of claim 12 wherein the least one hollow structural componentcomprises a first hollow structural component and a second hollowstructural component, wherein the first and second hollow structuralcomponents are designed to respond to pressure changes.
 17. The systemof claim 12 wherein the hollow structural component is placed outside ofthe centralizer.
 18. The system of claim 12 wherein the hollowstructural component is part of a strut of the centralizer unit.